1. Technical Field
The present invention generally relates to communication devices and in particular to communication devices designed with a multiple transmitter configuration to enable simultaneously transmissions.
2. Description of the Related Art
Communication devices supporting simultaneous voice and data, or multicarrier data, employ multiple simultaneously operating transmitters. These transmitters have to be isolated from each other to avoid intermodulation, which can cause receiver desensitization, spurious emissions, and other problems. Conventional designs of a multi-transmitter device include simultaneous voice and LTE (SVLTE) product transceivers, which employ radio frequency (RF) front end designs having notch filtering for isolating the simultaneous transmitters. For example, RF front end designs employ notch filters to isolate the voice transmit path from the data transmit path, in order to reduce intermodulation distortion. However, with these notch filter implementations, the notch filters have insertion loss which affects the transmitter output power and/or efficiency as well the receiver sensitivity. While the higher insertion loss can be okay in SVLTE mode, where some back-off of transmit power and degradation of receiver sensitivity is expected, the insertion loss affects the radio performance in non SVLTE operation, which is problematic. The degradation of radio performance becomes more severe in cases where the simultaneous transmitters occur at closer frequency spacing at which the notch filter insertion losses are higher, and is most severe for intraband simultaneous transmissions.
Carrier Aggregation (CA) products or devices have similar problems to the aforementioned SVLTE products, whereby simultaneous data transmission paths need to be isolated in order to minimize the generation of intermodulation distortion. Like in the SVLTE cases, fixed notch filter arrangements can be used for interband simultaneous data transmission carrier aggregation to isolate the transmit paths. However, in the intraband case, in which both data signals are in the same band, fixed notch filters cannot be utilized and/or are incapable of isolating the transmitters.